I get things like this. For me the answer is patience. Take a break, come back and try again.
If you are using the wysiwyg text editor, then highlight the text that you want to anchor your link to by pressing down on the left or appropriate mouse button and dragging the highlighting across that text; then take your finger off that button and go to the link icon and click on that to get the box to put the url in. Follow all the instructions there. Be patient.
Or, search this forum for how to do it using the html editing.